multimedia/mpv: address regressions from r402235 and r402236

• Remove INSTALLS_ICONS (see r395763 commit message)
• Set YTDL option as RUN_DEPENDS (see r402130 commit message)

PR: 202806
PR: 202337
PR: 204599
Reported by: jbeich
Approved by: cpm (implicit from bug 202337 and 202806 approvals)